This season also was the first year of the NBA's new divisional alignments, separating the league into six divisions of five teams instead of the previous four divisions of varying numbers of teams. As part of this realignment, the New Orleans Hornets moved from the Eastern Conference to the Western Conference.[1]

The current schedule format also debuted this season:

16 games against teams in the same division (four against each team)

24 games against six of the remaining conference teams combined, three from each division (four against each team)

12 games against the remaining four conference teams, two from each division (three against each team)

30 games against teams in the other conference (two against each team)

Over five seasons, each team will play each of the other conference teams outside its division a total of 18 times – 9 at home and 9 on the road.

Prior to the start of this season, Shaquille O'Neal was traded to the Miami Heat after his reported fallout with former Lakers teammate Kobe Bryant. Fans[who?] sensed this, along with the Pistonschampionship, as a possible end of dominance by the Western Conference. The Lakers also witnessed the loss of head coach Phil Jackson and replacement Rudy Tomjanovich as the Lakers missed out on the NBA playoffs for the fifth time in their history. However, the Western Conference has continued its domination in the regular season; since then, all playoff-bound teams in the West have either won 50 or more games, or were above .500 at the end of the season, in contrast to the Eastern Conference, where on average, three teams have had sub-.500 records.

During the off-season, the Phoenix Suns signed unrestricted free agent Steve Nash. With the addition of coach Mike D'Antoni and his offensive-minded strategy combined with Nash's play-making skills, Phoenix went on to win 33 games more than the year before. The Suns had the best overall record in the NBA, Nash won the MVP Award and D'Antoni won the Coach of the Year Award.

An early regular-season game between Detroit and Indiana at The Palace of Auburn Hills was disrupted with 45.9 seconds to go as a major altercation broke out between players and fans. This resulted in record-breaking suspensions, most notable of which was Ron Artest who received the longest suspension in NBA history (73 games plus the playoffs). The NBA also overhauled its league-wide security policy.

The Bulls made their first appearance in the playoffs since their 1998 championship season. The Bulls postseason berth followed an 0–9 start to the season with the Bulls having one of the youngest rosters in NBA history.

The Washington Wizards made their first appearance in the playoffs since the team name was changed for the 1997–98 season.

The Phoenix Suns started an unofficial league tradition of a mostly exposed hardwood floor, with a darker varnish on the outside of the three-point area. They also put their team's website name on the sideline, which other teams followed suit in the coming seasons. Through the 2010-11 NBA season, all of the teams, save the Oklahoma City Thunder, have placed their team websites on the sidelines.

The NBA Finals reached seven games for the first time since 1994 Houston Rockets vs New York Knicks

On Dec. 18, the Toronto Raptors traded 5 time all-star Vince Carter to the New Jersey Nets for Eric Williams, Aaron Williams, Alonzo Mourning and a pair of first-round draft picks. Mourning was bought out of his contract on February 11 and resigned with the Miami Heat being paid a second salary, the veteran's minimum.

Teams in bold advanced to the next round. The numbers to the left of each team indicate the team's seeding in its conference, and the numbers to the right indicate the number of games the team won in that round. The division champions are marked by an asterisk. Home court advantage does not necessarily belong to the higher-seeded team, but instead the team with the better regular season record; teams enjoying the home advantage are shown in italics.